device and method for recovering biogas

ABSTRACT

A device for recovering biogas, comprising at least one fermenter ( 13 ) and a percolate tank ( 10 ) for collecting the percolate removed from the fermenter or fermenters ( 13 ). The percolate tank ( 10 ) has a percolate inlet ( 10   c ) that can be connected to an outlet of the fermenter or fermenters ( 13 ) and a percolate outlet ( 10   b ). The percolate tank ( 10 ) is designed in such a way that the residence time of the percolate as it passes between the inlet ( 10   c ) and the outlet ( 10   b ) is sufficiently long to sanitize the percolate at the outlet ( 10   b ). The Percolate tank may also include one or more heaters to heat the percolate.

TECHNICAL FIELD

The invention relates to a device and a method for recovering biogas andmore particularly, to a system and method wherein a percolate tank,connected to one or more fermenters, is designed in such a way that theresidence time of the percolate as it passes between the inlet and theoutlet of the percolate tank is sufficiently long to sanitize thepercolate at the outlet.

BACKGROUND INFORMATION

During the methanization of biomass, fermenters are used in which afermentation process runs, wherein methane-containing gas is produced bythe fermentation of the biomass. A distinction is made between theso-called continuous process and the discontinuous process (batchprocess). In the latter, a percolate containing microorganisms isintroduced into a fermenter, which percolates through the substrate(biomass) and is collected in a percolate container and is re-introducedinto the fermenter, if necessary, until the biomass contained in thefermenter has been fermented. The fermented biomass is subsequentlyremoved from the fermenter and must be purified, if necessary, and beutilized in the customary manner. To facilitate the recovery, it may benecessary that the fermented biomass is sanitized. This means that thebiomass must be free of undesirable germs, bacteria, or otherimpurities, so that the fermentation residue can be recovered. The sameis also applicable for the percolate which likewise containscorresponding bacteria and the like and must likewise be sanitized so asnot to re-infect the already sanitized biomass in the fermenter duringrecycling.

SUMMARY

The object of the present invention therefore is to provide a device anda method of the type mentioned at the outset, with which a fermentationplant can be operated discontinuously without re-infecting the biomassin the fermenter.

The invention teaches that the residence time of the percolate in thepercolate tank is arranged such that the percolate is sanitized at thepercolate outlet of the percolate tank. For sanitization, the percolateis preferably heated in a heating section downstream of the percolateinlet of the percolate tank to a thermophilic temperature range oftypically between 48° C. and 60° C., preferably above 50° C. (othertemperatures, even below 50° C. are also possible, depending on thecircumstances and the microorganisms used) and is routed through thepercolate. For this purpose it is preferably provided that the flow pathis designed so that it meanders between the percolate inlet and thepercolate outlet, facilitating a particularly long residence time in thepercolate tank as a result of the extended distance at a temperaturethat is adjusted in the thermophilic range to ensure that only sanitizedpercolate can exclusively be removed at the percolate outlet, whichduring the percolation through the fermenter can no longer re-infect thebiomass present there.

According to a preferred embodiment, two sand traps are used, one ofwhich is exclusively supplied with sanitized percolate and one withnon-sanitized percolate. The feed from the fermenters used depends onwhether the fermenter provides sanitized or non-sanitized percolate atits outlet. The percolate that is in the sand trap for non-sanitizedpercolate is then supplied into the percolate tank, where it issanitized. The percolate that is in the sand trap for sanitizedpercolate can likewise overflow into the percolate tank and also entersthe percolate outlet in the sanitized state. In this context it isespecially advantageous to operate at least one fermenter in thethermophilic range, since the sanitization is then accomplished.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings wherein:

FIG. 1A—shows a part of a preferred embodiment for the device as taughtby the invention as a horizontal projection incorporating internalheaters;

FIG. 1B—shows a part of another embodiment for the device as taught bythe invention as a horizontal projection incorporating external heaters;and

FIG. 2—shows a cross-section through the device along a line I-I in FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment refers to allFigures equally.

The illustrated device preferably has a two-story design. In the upperstory (not shown in FIGS. 1A and 1B), one or a plurality of fermenters13 (see FIG. 2) are located into which a substrate of biomass to befermented is introduced. In the level lying below the fermenters 13, aplan view of which is represented in FIGS. 1A and 1B, a percolate tank10 is located which preferably has a plurality of chambers 1-6, which inthe embodiment shown are separated from each other by means of walls 10d, wherein the standing baffles 10 do not have a continuous design butmake it possible for the percolate to flow from one chamber (e.g. 6)into the respective adjacent chamber (e.g. 5). The walls 10 d arepreferably arranged such that a meandering flow path for the percolateresults from the percolate inlet 10 c in chamber 6 to the percolateoutlet 10 b in chamber 1, which is indicated by the arrows P. Otherforms of flow paths are also conceivable, which have a spiral or helicalshape, for example.

In the example shown, this level furthermore has two apparatuses thatare designed as sand traps for cleaning the percolate 11 and 12. Thisshows a sand trap for sanitized percolate (subsequently called “sandtrap ‘white’) and a sand trap for non-sanitized percolate 11,subsequently called “sand trap ‘black.’) As particularly shown in FIG.2, any percolate removed from the fermenters 13 can be fed into the sandtrap ‘black’ 12 (path P1) or into the sand trap ‘white’ 11 (path P2) viaa valve system 14, 15. From the sand trap ‘white’ 12, the percolate canflow through an opening or a standing baffle 16, which is designed highenough so that sanitized percolate from the sand trap ‘white’can enterinto a chamber 2 of the percolate tank 10 in the direction of the arrowP4, yet any backflow from the chamber 2 into the sand trap ‘white’ 12 isnot possible. For this purpose, the filling level F10 of the percolatein the percolate tank 10 is kept below the opening or the baffle wall 16and/or below the filling level F12 in the sand trap ‘white.’

From the sand trap ‘black’ 11, the percolate reaches the percolate tank10 via a percolate inlet 10 c, which can be designed as an opening or asa standing baffle, and then enters into the chamber 6. Same as above,the filling level F11 in the sand trap ‘black’ and/or the percolateinlet 10 c is also located above the filling level F10 in the percolatetank 10.

The plant now operates such that in each case percolate, which, in thefirst embodiment shown in FIG. 1A, enters chamber 6 of the percolatetank 10 (path P3) through the inlet 10 c, is initially heated by heaters15/17 (herein shown located in the first section 10 a facing the inlet10 c although this is not a limitation of the present invention) in aheating section. For this purpose, the temperature of the percolate ispreferably heated to a temperature in the thermophilic range ofgenerally between 48° C. and 60° C., whereafter it is routed in ameandering path (as illustrated by arrows P) through the individualchambers 6 through 1.

The path length P and the temperature of the percolate are adjusted suchthat exclusively sanitized percolate can be removed from the percolateoutlet 10 b in chamber 1, which can then be returned into the fermenters13, if necessary. One or more additional heaters in one or more chambersmay be provided such as for example heaters 19/21 in chamber 1.Alternatively, one or more heaters 23/25/27 may be provided outside thechambers 6-1 by providing one or more paths for example 29/31 throughwhich the percolate may flow and be heated before returning thepercolate to a chamber or sand trap as illustrated in the embodimentshown in FIG. 1B.

By returning the “warm” percolate at a temperature in a range ofpreferably above 50° C. into the fermenter 13, the substrate (biomass)which exists there is also gradually brought up to temperature until italso has a temperature in the thermophilic range after a certain periodof time (a few days), same as the percolate in the percolate tank. Bythe then thermophilic operation of the respective fermenter, the biomasscontained therein will also be sanitized, so that only sanitizedpercolate can be removed finally from the respective fermenter 13 and befed into the sand trap ‘white’ 12 via the path P2. As long as percolatethat is not yet sanitized is removed from the fermenter 13, this will befed into the sand trap ‘black’ via the path P1. This percolate from thislocation enters into the percolate tank and is routed to the percolateoutlet 10 b and is sanitized in this manner, as described above. Anypercolate from the sand trap ‘white’ 12 that has already been sanitizedis made available to the percolate circuit overflowing via the openingor the standing baffle 16.

A corresponding device can be operated as follows, for example: Biomassis placed into the fermenter 13 as substrate. This typically stays inthe fermenter 13 for a period between the input of the biomass until itsremoval, following fermentation of approximately 21 days. During itsinput, the material temperature corresponds to the ambient conditions,e.g. 10° C. Now the fermentation begins with starting the percolation ata percolate temperature of preferably higher than 50° C., preferably 53°C., wherein the percolate temperature is adjusted such that it reachessaid temperature value at the outlet 10 b of the percolate tank 10 atany time. For this purpose and for the adjustment of a correspondingtemperature value, additional heaters in the percolate tank 10 and/or inone of the two sand traps 11, 12, in the percolate tank 10, particularlyin the chambers 1 and 2, can be provided.

During this time, the percolate outflow from the fermenter is alwayssupplied into the sand trap ‘black’ 11 (arrow P1). During the course ofthe next days (e.g. up to about the 8th or the 9th day), a thermophilictemperature (preferably >50° C.) of the entire material in the fermenter13 is obtained at every location in the fermenter and/or the biomasscontained therein, by percolation with warm percolate. Consequently,also the material in the fermenter 13 is sanitized approximately afterthe 10th day, so that the percolate outflow also has a 100% sanitizedstatus. From this time on, the valve 14, 15 of the percolate of the flowis switched so that the percolate outflow enters the sand trap ‘white’(arrow P2).

The outflow from the sand trap ‘black’ 11 enters the percolate tank 10in the area of the chamber 6 via the inlet 10 c. Because of the feedfrom the not yet completely sanitized contents of the fermenters 13, thetemperature at this location will always be less than the temperature(approx. 53° C.) provided for the percolate removal. By heating thechambers (in particular chamber 6 in the heating section 10 a) thepercolate is preferably heated to 53° C. and is kept at this temperaturein the percolate tank 10 along the entire flow path and/or for theentire residence time. Because the percolate flows slowly through thechambers 6 to 1, the percolate is preferably completely sanitized in thevicinity of chambers 3 and 2 after a defined time (e.g. approximatelyafter 5 to 8 days residence time, calculated from the time of entry intochamber 6). At this point, now also the percolate from the outflow 16 ofthe sand trap ‘white’ is likewise supplied into the percolate tank 10,which results in that the volumetric flow rate increases after the inletpoint.

The two sand traps 11, 12 are preferably always filled 100% up to theheight of the overflow weir of the openings 16 and 10 c. The water levelF10 in the percolate tank 10 must always be lower in relation to this inorder to prevent a back flow from the percolate tank 10 back into thesand traps 11, 12 (particularly into the sand trap ‘white’ 12). A levelcontrol is preferably provided for this purpose.

The temperatures mentioned here and particularly the times mentioned areselected as examples and can deviate in practice.

Modifications and substitutions by one of ordinary skill in the art areconsidered to be within the scope of the present invention, which is notto be limited except by the allowed claims and their legal equivalents.

1. A device for recovering biogas, comprising at least one fermenter(13) and a percolate tank (10) for collecting the percolate from the atleast one fermenter (13), wherein the percolate tank (10) has apercolate inlet (10 c) that can be connected to an outlet of the atleast one fermenter (13) and a percolate outlet (10 b), characterized inthat the percolate tank (10) is designed such that the residence time ofthe percolate as it passes between the inlet (10 c) and the outlet (10b) is sufficiently long so that the percolate is sanitized at the outlet(10 b).
 2. A device according to claim 1, characterized in that thepercolate tank (10) has a meander-shaped flow path (P) between the inlet(10 c) and the outlet (10 b).
 3. A device according to claim 1,characterized in that the percolate tank (10) is arranged below the atleast one fermenter (13).
 4. A device according to claim 1,characterized in that a plurality of fermenters (13) are provided ofwhich at least one is designed for an at least temporary thermophilicoperation.
 5. A device according to claim 4, characterized in thatbetween the at least one fermenter (13) and the percolate tank (10) atleast one apparatus (11, 12) is connected for cleaning the percolate. 6.The device according to claim 4, characterized in that at least twoapparatuses (11) and (12) are provided for cleaning the percolate,wherein fermenters (13) and the apparatuses (11) and (12) can beconnected such that sterilized percolate coming from a fermenter (13) issupplied into the one apparatus (12) and that non-sanitized percolatecoming from a fermenter (13) is respectively provided into the otherapparatus (11).
 7. A device according to claim 1, characterized in thatat least one heating section (10 a) is provided in the percolate tank(10) downstream of the percolate inlet (10 c), in which the percolatethat is entering the percolate tank (10) can be heated to a specifiedtemperature.
 8. A device according to claim 6, characterized in that atleast one of the apparatuses (11) and (12) is a sand trap.
 9. A deviceaccording to claim 6, characterized in that in the percolate tank (10)and/or in one and/or in both of the apparatuses (11, 12) a heater isprovided for cleaning the percolate which can be operated so that aspecified minimum temperature of the percolate is adjusted.
 10. A methodfor the recovery of biogas with which substrate is percolated withpercolate in at least one fermenter (13) and that percolate after thepercolation enters into a percolate tank (10), wherein the percolatetank (10) has a percolate inlet (10 c) that can be connected with anoutlet of the at least one fermenter (13) and a percolate outlet (10 b),characterized in that the percolate passes (10) between the inlet (10 c)and the outlet (10 b) is routed such that the residence time of thepercolate as it passes between the inlet and the outlet is sufficientlylong so that the percolate at the outlet (10 b) is sanitized.
 11. Themethod according to claim 10, characterized in that the percolate isrouted meander-shaped in the percolate tank.
 12. The method according toclaim 10, characterized in that a plurality of fermenters (13) are used,at least one of which is operated thermophilically at least temporarily.13. The method according to claim 10, characterized in that between theat least one fermenter (13) and the percolate tank (10) the percolate isrouted through at least one apparatus (11, 12) for cleaning thepercolate.
 14. The method according to claim 10, characterized in thatat least two apparatuses (11) and (12) are provided for cleaning thepercolate, wherein sanitized percolate from a fermenter (13) is routedinto the one apparatus (11) and non-sanitized percolate from a fermenter(13) is routed respectively into the other apparatus (12).
 15. Themethod according to claim 10, characterized in that a specifiedtemperature is adjusted in the percolate tank (10) downstream of thepercolate inlet (10 c).
 16. The method according to claim 13,characterized in that at least one of the apparatuses (11) and (12) is asand trap.
 17. The method according to claim 13, characterized in thatthe percolate in the percolate tank (10) and/or in the one and/or inboth of the apparatuses (11, 12) for cleaning the percolate is heatedsuch that a specified minimum temperature of the percolate is adjusted.